Heat abstracting and shielding means for electron discharge devices



Aprll 19, 1960 J cHlsLow 2,933,292

HEAT ABSTRACTING AND SHIELDING MEANS FOR ELECTRON DISCHARGE DEVICESFiled Dec. 2, 1955 2 .wheets-Sheet 1 FIG. 3

1 iNVE/VTOR J. H. C HIS L 0W BY 994M cmw ATTORNEY April 9, 1960 J. H.CHISLOW 2,933,292

HEAT ABSTRACTING AND SHIELDING MEANS FOR ELECTRON DISCHARGE DEVICESFiled Dec, 2, 1955 2 Sheets-Sheet 2 CFM BARE ENVELOPE WITH SHIELD FIG. 5

l/VVENTOR J. H. CHIS L 0W ATTORNEY United States atent HEAT ABSTRACTINGAND SHEELDING MEANS FOR ELECTRGN DISCHARGE DEVICES Joseph H. Chislow,New York, N.Y., assignor to Bell Telephone Laboratories, Incorporated,New York, N. a corporation of New York Application December 2, 1955,Serial 550,744 4 Claims. (Cl. 257-263) This invention relates to thecooling of electron discharge devices and particularly to heatconducting shields to increase the dissipation of heat from suchdevices.

It is well known that the problem of heat abstraction from vacuum tubesis a formidable one as the life of vacuum tubes is considerably reducedat elevated envelope temperatures. Furthermore, vacuum tubes operate inconjunction with and adjacent to circuit components such as resistors,capacitors, inductors, et cetera, whose predictable life is a functionof operating temperature, and, accordingly, heat from vacuum tubes hasan adverse effect on the lifetimes of these components.

Abstraction of the heat generated within a vacuum tube when operating isdependent on radiation, convection, and conduction. The heat lossthrough radiation is not significant, nor generally is that throughconduction, as the vacuum tube envelope is not in good thermalconductive engagement with any other body, and heat dissipation byconvection by forced draft ventilation requires some accessory equipmentincludin a blower. Priorly it has been proposed to reduce thetemperature of the envelopes of vacuum tubes by forced air coolingcoupled with the use of tube heat shields. Particularly when many tubeswere mounted in relatively confined spaces, it was found that heatshields alone were not sufficient to reduce envelope temperatures to thepoint needed for optimum component reliability. Various heat shieldshave been proposed to reduce the required forced-airf'eed supply size.These shields have generally conducted heat from the vacuum tubeenvelope to a chassis or base which accordingly served as a heat sink.However, the distribution of heat over the envelope of a vacuum tube isnot even, generally being a maximum directly adjacent the anode, or, inthe case of multi-element tubes, midway between the two anodestructures. Therefore heat was conducted from the relatively coolerupper portions of the envelope to the base past the hotter portions ofthe envelope. Accordingly these conductive paths had a high thermalresistance and the heat being conducted to the base or chassis resultedin further heat concentrations at the hotter portions of the tubeenvelope.

It is one object of this invention to increase the life of electrondischarge devices. It is a further object of this invention to increasethe abstraction of heat by conduction from vacuum tubes such that theforced-air-feed supply size is either greatly reduced or the need forsuch cooling supply is obviated. It is a still further object of thisinvention to substantially lower the temperature of the envelope of anelectron tube by increasing the conduction of heat therefrom.

Another object of this invention is to provide a metallic heat transferpath from the envelope of an electron discharge device to a chassismember wherein heat is conducted away from the envelope by the shortestpossible path thereby preventing the heat being conducted from itselfadding to the temperature of the tube envelope.

A still further object of this invention is to provide a tube shield inintimate thermal conductive engagement with substantially the entireenvelope of the electron discharge device and with the chassis so as toincrease the heat conducted from the envelope to the chassis.

A further object of this invention is to provide a tube shield the shapeof which assists in developing turbulence in the air flow such that thecooling effect of convection is enhanced.

These and other objects of this invention are achieved by positioning anelectron discharge device or a vacuum tube within a heat conductingshield. The shield fits snugly over the tube insuring firm, continuouscontact over substantially the entire outer surface of the tubeenvelope. The shield is secured to a good heat conduction base orchassis tube mounting assembly acting as a heat sink by means of aflange portion extending substantially the height of the shield. Thus,it is a feature of this invention that circumferential heat conductionis provided from the tube envelope to the heat sink and concentrationsof heat as found in conventional shields which conduct in an axialdirection to the tube base or top are avoided. The circumferential heatflow may conven iently be represented by a multiplicity of parallelcircumferential heat conducting paths.

The envelopes of tubes can generally be considered to be cylindrical,but actually in the mass production of them, the envelopes, instead ofbeing circular in cross section, are more nearly oval or elliptical. Theheat conducting shield, however, is resilient enough to allow forconsiderable variations without any loss of contact points with theenvelope of the tube. Thus, it is a further feature of this inventionthat the resilient metal roll fits over the vacuum tube such thatconsiderable variations in the diameter and concentricity of the tubeenvelope can be accepted without loss of any points of thermal contactwith the heat conducting shield.

The heat conducting shield, in one specific embodiment, comprises asubstantially rectangular sheet of metal rolled up with a slight overlapand terminating in an outwardly projecting flange portion forfrictionally embracing a good heat dissipating base or mountingassembly. The shield has a tab portion to facilitate sliding the shieldon and off the electron discharge device. Thus, in accordance withaspects of this invention, a vacuum tube shield is provided that issimple in construction, inexpensive to manufacture, and easily mounted.

The shield serves a dual function as it not only effectively removes theheat of the tube to the heat dissipating base or mounting assembly, inaccordance with this invention, but also it acts as an electrostatic andelectromagnetic shield, as is well known and as is generally necessaryfor many tube applications.

A complete understanding of the invention and of these and otherfeatures and advantages thereof may be gained from consideration of thefollowing detailed description in conjunction with the accompanyingdrawing, in which:

Fig. l is a perspective view of a heat conducting shield, iilustrativeof one specific embodiment of this invention, mounted on a heatdissipatin plate and with a vacuum tube positioned therein;

Fig. 2 is a plan view of the assembly of Fig. 1;

Fig. 3 is a plan view of just the heat conducting shield of theembodiment of Fig. 1;

Fig. 4 is a graph of tube envelope temperature above ambient as afunction of air fiow; and

Fig. 5 is a perspective view of a modification of a mounted heatconducting shield made in accordance with the principles of the presentinvention.

Referring now to Fig. l, the shield 10 is a hollow cylinder rolled froma thin resilient metallic material so as to fit snugly around anelectron discharge device insur ing firm, continuous contact oversubstantially the entire outer surface of the envelope of the device;the shield itself is best seen in Fig. 3. A typical electron dischargedevice or vacuum tube 11 is shown within and in good thermal conductivecontact with the shield 10. The tab portion 25 is an integral part ofthe shield and serves to facilitate sliding the shield 10 on and off thevacuum tube 11. The shield 10 may advantageously be of beryllium copperfor this alloy exhibits heat conductive properties and is sufficientlyresilient when formed into the shield 10 to grip the vacuum tube 11making good heat conductive engagement therewith.

The vacuum tube lll with the shield 10 around it is positioned on themetallic mounting assembly 12. The flanged portion 113 of the rolledcylinder is formed so as to engage the tongue plate 14 of the mountingassembly 12 in intimate contact and thus provide a good heat conductivepath from the shield 10 to the tongue plate 14.

The slot 24 provides a region of high compliance for the purpose of easyinsertion and removal of theshield, and precludes the possibility ofdistorting critical mating surfaces by the insertion or the removal ofthe shield 10. Thus, the continuity of heat abstractive contact of theshield it) with the vacuum tube 11 is assured irrespective of thefrequency of insertions and removals.

Referring now to Fig. 2, one side 15 of the tongue plate 14 of themounting assembly 12 is seen to be in intimate contact with the flangedportion 13 of the shield while it other side 16 is in contact with aportion of the shield 10 outer surface. As well as being the body towhich the vacuum tube 11 thermal energy is conducted by means of theshield 10, the tongue plate 14 effectively serves tomaintain the shield10 about the vacuum tube 11 in a mechanically secure manner.

Referring now to Fig. 4, there is graphically shown the effectiveness ofthe shield 10 in conducting heat from the vacuum tube Ill envelope. Thescale of the vertical axis is centigrade degrees temperature rise of thevacuum tube envelope above ambientQand the scale of the horizontal axisis cubic feet per minute delivery air fiow past the vacuum tubeenvelope. The upper curve 20 represents an unshielded vacuum tubeenvelope temperature rise above ambient as a function of delivery airflow, and the lower curve 21 represents a heat shielded vacuum tubeenvelope temperature rise above ambient as a function of delivery airflow when the tube is shielded with the embodiment of Fig. 1. It appearsclearly that the shield 10 greatly reduces the forced air feedsupplysize required to maintain a given envelope temperature.

In one specific embodiment of this invention for use with novel vacuumtubes the shield 10 was rolled from 0.010 inch beryllium copper alloystrip. hard strip was annealed to hard, then cut and rolled, and thenheat-treated back to hard. Before rolling, the shield 10 measured 3%inches long and 1% inches high with the tab portion 25 extending anadditional ,4, inch in height, and when rolled formed a hollow cylinderinch in diameter. The mounting assembly 12 was made of 0.064 inchaluminum alloy sheet. The beryllium copper shield 10 had a 0.0002 inchthick coating of tin electrodeposited upon it. The additive finish oftin reduced the formation of oxide films on the shield. This wasdesirable because these films exhibit a higher resistance to theconduction of thermal energy than does the shield 10 material. Further,the tin finish resulted in a smaller galvanic couple between the shield10 and the aluminum mounting assembly 12, than that formed between anunplated shield and the mounting assembly 12. Still further, the tipplate reduced the interface coefiicient between the envelope of thevacuum tube 11 and the shield 10, thus resulting in better heat transferbetween these bodies.

Referring now to Fig. 5, there is shown a modification of a heat shieldaccording to the invention. The modification differs from theillustrative embodiment of the invention shown in Fig. 1 in that theflange portion 21 is straight rather than stepped and is secured to achassis or heat sink member 22 by fastening means. In the embodimentshown in Fig. 5 rivets were used. The shield 23 was made from berylliumcopper alloy strip and had a 0.0002 inch layer of tin electrodepositedupon it.

Embodiments of this invention display excellent heat dissipationproperties. Although the underlapped, resilient, metal cylinder may beeasily slid on or off an electron discharge device, the cylindersecurely grips substantially the entire exterior surface of the devicesuch that heat transfer is not retarded by air entrapped between theexterior surface and the shield, and such that a multiplicity of direct,circumferential, high thermal conductivity paths is provided from theexterior surface to a heat dissipating chassis member.

It is to be understood that the above-described arrangements areillustrative and not restrictive of the principles of the invention.Other arrangements may be devised by those skilled in the art withoutdeparting from thc'spirit and scope of the invention.

What is claimed is:

1. Apparatus for conducting heat from the envelope of an electrondischarge device to a chassis including a tongue plate mountng member,said apparatus comprising a resilient metal tubular member of a lengthsubstantially as great as that of the electron discharge device,

the discharge device being slidably positionable within said tubularmember so that saidtubular member grips the envelope of the device insecure heat conductive en:

g'agement, said tubular member having a tab portion extending from thewall thereof substantially beyond the end of said vacuum tube, saidtubular member having an inner underlapping portion,.and also a flangeportion of approximately the same length as said tubular memberextending away from and then parallel to the outer surface thereof so asto substantially parallel said outer surface atv a distance therefrom,said tongue plate being positioned between and in physical contact withsaid flange portion and said outer surface so that heat flow in saidtubular member occurs along a circumferential path approximatelyperpendicular to its axis and heat transfer from said tubular member tosaid tongue plate occurs by conduction.

2. Apparatus for abstracting heat from the envelope of.

an electron discharge device comprising in combination a heatdissipating mounting member and a resilient heat conducting tubularmember, the electron discharge device being slidably positionable withinsaid tubular member.

and said tubular member being so dimensioned as to completely encloseand grip substantially the entire envelope of the electron dischargedevice in secure heat conductive engagement, said tubular member havinga longitudinal overlapping portion and an underlapping portion in heatconductive engagement with each other, said overlapping portionextending away from and then parallel to the outer surface of saidtubular member to define a flange portion, said mounting member having atongue portion extending along the length of and adiacent to saidtubular member, said tongue portion being positioned between the innersurface of said flange portion and the outer surface of said tubularmember in secure heat conductive engagement therewith so that heat flowin said tubular member occurs along a circumferential path approximatelyperpendicular to its axis and heat transfer from said tubular member tosaid mounting member occurs by conduction between the surfaces thereof.

3. Means for abstracting heat from the surface of an electron dischargedevice comprising a heat dissipating base and a resilient heatconducting hollow cylinder having overlapping longitudinal portions inintimate heat conductive engagement with each other, said cylinder beingadapted to be positioned over the electron discharge device in intimateheat conductive engagment with substantially the entire surface thereofso that heat transfer from the electron discharge device to saidcylinder occurs by conduction, said cylinder further having alongitudinal flange portionextending away from its outside surface, saidheat dissipating base having a tongue portion extending along the lengthof and adjacent to said cylinder, said tongue portion being secured inintimate heat conductive engagement with a surface of said flangeportion so that heat flow in said cylinder occurs along acircumferential path approximately perpendicular to its axis and heattransfer from said flange portion to said base occurs by conduction.

4. Means for abstracting heat from the surface of a heat generatingelectrical device comprising a heat dissipating base member and athermally conductive sleeve member having overlapping longitudinal edgessuch that the diameter of said sleeve member is variable, said sleevemember being adapted to be positioned over the electrical device and inintimate heat conductive engagement with the surface thereof so thatheat transfer from the electrical device to said sleeve member occurs byconduction, said sleeve member having further a longitudinal flangeportion extending away from its outside surface, said base member havinga tongue portion extending along the length of and adjacent to saidsleeve member, said tongue portion being secured in intimate heatconductive engagement with a surface of said flange portion so that heatflow in said sleeve member occurs along a circumferential pathapproximately perpendicular to its axis and heat transfer from saidflange portion to said base member occurs by conduction.

References Cited in the file of this patent UNITED STATES PATENTS261,473 Naughten July 18, 1882 985,094 Zachara Feb. 21, 1911 2,176,657Finch Oct. 17, 1939 2,388,848 Howe Nov. 13, 1945 2,646,460 Del Camp July21, 1953 2,662,220 Saari Dec. 8, 1953 2,771,278 Slack Nov. 20, 19562,820,082 Gray et al. Jan. 14, 1958

